Misfire detection method and control unit for an internal combustion engine

Abstract

The invention relates to a misfire detection method for an internal combustion engine, in particular for a stationary gas engine for power generation, comprising the steps of determining whether the engine is subjected to an unexpected performance change (S4) and detecting a misfire condition of the engine by attributing the unexpected performance change to be caused by a misfire during operation of the engine (S6).

Description

TECHNICAL FIELD

[0001] The present invention relates to a misfire detection method for an internal combustion engine, in particular for a stationary gas engine for power generation, and to a control unit of an internal combustion engine for performing such misfire detection method. BACKGROUND

[0002] In order to ensure high efficiency, internal combustion engines are designed to burn the air-fuel mixture within their cylinders in a timing-controlled manner so as to form a peak pressure in their cylinders at the ideal time under ideal operating conditions in order to maximize the work recovered from the expanding gases produced by the combustion. To this end, the ignition of the air-fuel mixture and the propagation of the flame front within the combustion chamber must take place according to a strictly defined pattern. However, any deviation from the ideal operating conditions can lead to less advantageous combustion of the air-fuel mixture and thus to a deterioration of the performance and efficiency of the engine.

[0003] During operation, the engine, i.e. its individual cylinders, can suffer from bad or no combustion so that no significant energy conversion takes place and thus no significant pressure and temperature rise is experienced in the individual cylinder. These undesired and unexpected phenomena constitute a malfunction of the engine and can generally be referred to as misfire or combustion misfire.

[0004] Combustion misfire can be caused by many different reasons. For example, a malfunction of the ignition system, i.e. of the spark plug, can lead to bad or no combustion in an individual cylinder of the engine. Alternatively, the intake system of the engine can suffer from a malfunction so that the air-fuel mixture fed into the combustion chamber of the engine has an unfavorable composition, e.g. has an air-fuel ratio which lies outside the flammable range.

[0005] In addition to the deterioration of the performance and efficiency of the engine, misfire can lead to unburned fuel entering the exhaust system of the engine. In this way, misfire can lead to damage of a catalytic converter present in the exhaust system and to environmental pollution when unburned fuel is emitted into the environment through the exhaust system.

[0006] From the prior art, it is known to identify a continuous misfire condition within an individual cylinder, i.e. a misfire which continuously occurs in subsequent operating cycles of the engine, e.g. by identifying a defective spark plug of the ignition system. However, the known methods are not suitable to detect a malfunction condition which occurs intermittently or only during a certain number of operating cycles, i.e. a phenomenon of intermittent or intermittent misfire. SUMMARY

[0007] Starting from the prior art, it was an object to provide an improved misfire detection method for an internal combustion engine and a control unit of an internal combustion engine for performing such method.

[0008] This object is achieved by the misfire detection method and the control unit described in the following.

[0009] Therefore, a misfire detection method for an internal combustion engine, in particular for a stationary gas engine used for power generation, is provided. The method comprises the steps of determining an operating mode of the engine, wherein the operating mode corresponds to a grid parallel operation mode operation or an island operation mode; acquiring a power measurement signal of the engine via an engine output power sensor when the operating mode corresponds to the grid parallel operation mode or acquiring a power measurement signal and a speed measurement signal of the engine via the engine output power sensor and an engine speed sensor when the operating mode corresponds to the island operation mode; determining whether the engine is subject to an unintended performance change based on the power measurement signal when the operating mode corresponds to the grid parallel operation mode or based on the power measurement signal and the speed measurement signal when the operating mode corresponds to the island operation mode; and detecting a misfire condition of the engine by attributing the unintended performance change to a misfire during operation of the engine.

[0010] Furthermore, a control unit for misfire detection of an internal combustion engine, in particular of a stationary gas engine, is provided. The proposed control unit is in communication with an engine output power sensor and an engine speed sensor and is configured to perform the misfire detection method as described above. Therefore, the technical features described in connection with the misfire detection method in the present disclosure can also refer to and apply to the proposed control unit and vice versa. In particular, the control unit is configured to determine an unintended performance change of the engine and to detect a misfire condition of the engine by attributing the unintended performance change to a misfire during operation of the engine. BRIEF DESCRIPTION OF DRAWINGS

[0011] The present disclosure will be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 A power generation unit equipped with an internal combustion engine in the form of a stationary gas engine is schematically illustrated;

[0013] Figure 2 A flowchart schematically illustrating a misfire detection method for detecting a misfire occurring in an internal combustion engine is schematically illustrated;

[0014] Figure 3 A general procedure for the step of determining whether an internal combustion engine is subject to an unintended performance change performed during the method depicted in Figure 2

[0015] Figure 4 and Figure 5 ​More detailed Figure 3 the steps depicted; and

[0016] Figure 6 The general procedure of the steps performed for validating the measurement signal during the method depicted in Figure 2 DETAILED DESCRIPTION

[0017] Hereinafter, the present application will be explained in more detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and repetitive description thereof can be omitted to avoid redundancy.

[0018] Figure 1 A power generation unit 10 for generating electric power to be supplied to an electric grid 12 is schematically shown. The electric grid 12 can have any suitable size and may, for example, be a decentralized or nationwide electric grid connected to a plurality of power generation units, but is not limited to this configuration. Rather, in one configuration, the electric grid 12 can be equipped with electric power generated by only one power generation unit. The power generation unit 10 can constitute or be part of a power plant and comprises at least one electric generator 14 driven by an internal combustion engine 16 (hereinafter also referred to as "engine") to convert mechanical energy into electric power fed to the electric grid 12. The electric generator 14 is thus electrically connected to the electric grid 12 and is coupled to the internal combustion engine 16 in a torque-transmitting manner. In particular, the electric generator 14 is coupled to an output shaft 18 of the engine 16 such that the electric generator 14 is actuated by the output shaft 18 during operation of the engine 16.

[0019] The power generation unit 10 is configured to be operated in different operating modes. In particular, the power generation unit 10 can be operated in a grid-parallel operating mode and an island operating mode.

[0020] The grid-parallel operating mode refers to a mode in which the power generation unit 10 is operated in parallel with the electric grid 12, in particular constituted by a national or local distribution network, which has a greater capacity compared to the power generation unit 10. This means that in this mode the individual electric power output by the power generation unit 10 is small compared to the load on the electric grid 12. Accordingly, the frequency of the electric power supply should be considered to be fixed by the electric grid 12. In this mode, the engine 16 of the power generation unit 10 is typically operated at a constant speed depending on the frequency set by the electric grid 12.

[0021] The island operating mode refers to a mode in which the power generation unit 10 is operated isolated from the national or local distribution network. In this mode, the engine 16 of the power generation unit 10 sets the characteristics of the electric power fed to the electric grid 12. For example, by changing the engine speed of the engine 16, the frequency of the electric current flowing through the electric grid 12 can be adjusted.

[0022] ​The engine 16 is an internal combustion engine, in particular a reciprocating engine in the form of a stationary gas engine, which is powered with a fuel-air mixture of gaseous fuel and air, such as a mixture of natural gas and air. The engine 16 preferably comprises a plurality of cylinders, such as eight or twelve or eighteen cylinders, which can be arranged according to a straight engine configuration, a V-configuration or any other known cylinder configuration. In one configuration, fresh air can be mixed with a fuel medium to create an air-fuel mixture before entering the combustion chamber. Alternatively, fresh air and fuel medium can be supplied separately into the combustion chamber and thus mixed within the combustion chamber, e.g. by means of a fuel pump injecting the fuel medium into the combustion chamber.

[0023] Each cylinder is provided with a combustion chamber delimited by a piston accommodated in the cylinder. The piston is configured for reciprocating and axial movement within the cylinder and is coupled to a crankshaft of the engine such that the reciprocating movement of the piston is converted into a rotational movement of the crankshaft.

[0024] During operation of the engine 16, an air-fuel mixture is supplied to and ignited in each cylinder in order to create a high-temperature and high-pressure gas which exerts a force to the associated piston and thus axially moves the associated piston, rotating the crankshaft and thus the output shaft 18 which is coupled to the crankshaft in a torque-transmitting manner. In this way, chemical energy is first converted into mechanical energy driving the output shaft 18 of the generator 14, which is then converted into electrical energy by means of the generator 14.

[0025] The engine 16 further comprises a control unit 20, also referred to as “engine control unit” or “engine control module”, which is configured to control and monitor the operation of the engine 16. In particular, the control unit 20 is of the electronic control unit type and is configured to read out measurement data from a plurality of sensors monitoring various engine operation parameters. Furthermore, the control unit 20 is configured to process and interpret the measurement data thus acquired and, in response, control the actuation of a plurality of engine actuators, e.g. by controlling the ignition characteristics, such as the amount and composition of the air-fuel mixture to be fed to and ignited in the combustion chamber, the ignition timing, the valve actuation and timing, etc., in order to set and adjust the operating point of the engine.

[0026] The basic structure and function of such an internal combustion engine 16 and its components, in particular the control unit 20, are well known to the person skilled in the art and are therefore not further explained. Instead, the misfire detection method, also referred to as “method”, in the present disclosure, which is interconnected with the present invention to detect a misfire condition during operation of the engine 16, is discussed in the following.

[0027] In the context of the present disclosure, the terms "misfire condition", "misfire" or "combustion misfire" refer to any undesired and unintended deterioration of the combustion process occurring in at least one cylinder of the engine affecting the performance or efficiency of the engine during an operating cycle. This can be the case, for example, when no combustion or a poor combustion occurs in at least one cylinder. A poor combustion can refer to an operating cycle in which the air-fuel mixture is not completely combusted and / or the flame front produced by the air-fuel mixture present in the cylinder at the time of ignition does not spread in the desired manner and / or the combustion ignites at a desired timing.

[0028] The proposed method is suitable for detecting different types of misfire phenomena and conditions, such as continuous, intermittent and single misfire events. In particular, the term "continuous misfire" refers to a fault condition of a cylinder in which misfire occurs continuously, i.e. in subsequent operating cycles of the engine. The term "intermittent misfire" refers to a fault condition of a cylinder in which misfire occurs intermittently in subsequent operating cycles. In other words, in a cylinder affected by such a fault, proper operating conditions and misfire conditions can alternate. Furthermore, the term "single misfire" can refer to a fault condition of a cylinder in which misfire occurs as a single event, i.e. only for one or more subsequent operating cycles of the engine.

[0029] In the illustrated configuration, the control unit 20 is configured to perform a misfire detection method. In the following, reference is made to Figures 2 to 6 The misfire detection method is described, the figure illustrating the method in the form of a flowchart. First, reference is made to Figure 2 The general method is described, the figure showing an overview of the method by illustrating the individual method steps and their interaction. Then, reference is made to Figures 3 to 6 The individual method steps and their underlying procedures are specified.

[0030] Upon starting the method, the control unit 20 determines in a first step S1 in which operating mode the power generation unit 10, in particular the engine 16, is operated. More specifically, the control unit 20 determines whether the power generation unit 10, in particular the engine 16, is in a grid parallel operating mode or in an island operating mode. As will be described in the following, further steps of the method, such as steps S4, S5 and S6, can be performed or can vary depending on the determined operating mode.

[0031] Thereafter, the method proceeds to step S2, from which a routine or loop consisting of method steps S2 to S7 is initiated and iterated. In the following, the routine or loop consisting of steps S2 to S7 is referred to as the "loop". The loop is initiated by or at a predetermined repetition event. This means that the loop is initiated repeatedly after a predetermined time period or event. Preferably, the loop is executed during at least one operating cycle of the engine. Generally, the term "operating cycle" refers to a combustion cycle of one cylinder, which comprises the following steps: supplying an air-fuel mixture into the cylinder; combusting the air-fuel mixture; and subsequently expelling exhaust gases from the engine. Typically, the operating cycle is associated with one or more piston strokes within the cylinder. In one configuration, the loop can be initiated or executed for each operating cycle of each cylinder.

[0032] In step S2, the control unit 20 retrieves or determines whether the power generation unit 10, in particular the engine 16, has reached a predetermined operating state, i.e. a warm-up or a mature operating state. In this way, it can be ensured that the engine 16 has reached a stable operating point at which the engine can be operated under stable conditions and efficiently. The predetermined operating state can further serve as a reference state of the engine 16, which allows for an efficient evaluation of the operation of the engine, i.e. whether the engine 16 is subject to misfire conditions. The predetermined operating state can depend on the operating mode of the engine 16. In this step, the control unit 20 can monitor at least one engine operating parameter, such as the engine speed, the engine temperature, etc., and determine that the engine is in a mature state when at least one or each of the at least one operating parameter has reached a predetermined threshold or lies within a predetermined range.

[0033] If it is determined that the engine 16 is not in its mature state, the further execution of the loop is interrupted and the method returns to the beginning of the loop, i.e. to step S2. However, upon determining that the engine 16 is operated in the predetermined operating state, i.e. the mature state, the method proceeds to a third step S3, in which the control unit 20 monitors the operation of the engine 16, i.e. the performance and the functionality of the engine 16. To this end, the control unit 20 receives a plurality of measurement signals indicative of engine operating parameters.

[0034] In the context of the present disclosure, the term "engine operating parameter" refers to any parameter suitable to quantify the performance and the operation of the engine, such as the operating point of the engine. For example, in the illustrated configuration, the engine operating parameter refers to at least one of the engine speed, the engine load, the power output by the engine, the pressure prevailing in the engine, such as the intake manifold pressure and the differential pressure at the throttle of the engine.

[0035] In particular, for monitoring the operating conditions of the engine 16, the control unit 20 is connected to at least one sensor unit configured to measure engine operating parameters and transmit to the control unit 20 measurement signals indicative of the measured parameters.

[0036] Thereafter, the method proceeds to each of steps S4 and S5 performed on the basis of the data acquired in step S3. In the illustrated configuration, steps S4 and S5 are performed in parallel. Alternatively, these steps can be performed subsequently, i.e. one after the other in any order. Moreover, step S3 can be performed together with or in parallel with each of steps S4 and S5.

[0037] Step S4 is provided to determine whether the engine 16 is subject to an unexpected change in performance, in particular an unexpected decrease in performance. This step refers to an associated time period. In other words, during this step, the control unit 20 determines whether the engine 16 is subject to or has been subject to an unexpected change in performance during the associated time period. To this end, the control unit 20 analyses the data acquired during step S3, which are indicative of the performance or functioning of the engine during the associated time period.

[0038] In particular, the time period associated with step S4 can refer to one or more subsequent operating cycles of the engine 16. In other words, the step of determining whether the engine 16 is subject to an unexpected change in performance is associated with at least one operating cycle of the engine 16.

[0039] More specifically, step S4 of determining whether the engine is subject to an unexpected change in performance is performed to determine whether the output torque of the engine is unexpectedly changed. Thus, during this step, the measurement signals indicative of the output torque of the engine 16 can be analysed.

[0040] By way of illustration of sub-steps S4.1 to S.4.5 and their interactions, the general procedure of step S4 is depicted in Figure 4 In a first sub-step S4.1, the control unit 20 obtains or reads at least one measurement signal received during step S3. It is noted that steps S3 and S4.1 can be performed in one common step or can constitute one common step.

[0041] In the illustrated configuration, during sub-step S4.1 the control unit 20 obtains a first measurement signal 22 indicative of the engine power output by the engine 16 during operation, also referred to as engine performance. In particular, the first measurement signal 22 can be indicative of the actual engine performance, i.e. the engine performance output during the associated time period or operating cycle. In other words, based on the first measurement signal 22, the actual power or performance output by the engine 16, i.e. associated with the time period under consideration, can be derived. The first measurement signal 22 is therefore also referred to as power measurement signal.

[0042] In order to obtain the first measurement signal 22, the control unit 20 makes use of a first sensor unit 24 coupled to the generator 14. In particular, the first sensor unit 24 performs current transformer measurements and voltage transformer measurements at the generator 14 and based thereon generates the first measurement signal 22 indicative of the actual power or performance output by the engine 16.

[0043] Furthermore, the control unit 20 obtains a second measurement signal 26 indicative of the engine speed, i.e. indicative of the rotational frequency of the crankshaft and / or camshaft of the engine, in particular the number of rotations of the crankshaft and / or camshaft per unit of time. The second measurement signal 26, also referred to as engine speed signal, is generated by means of a second sensor unit 28 provided in the form of at least one pick-up sensor coupled to the crankshaft and / or camshaft and transmitted to the control unit 20.

[0044] Then, in sub-step S4.2, the control unit 20 is configured to process the received measurement signals to generate at least one processed signal. To this end, the control unit 20 can be configured to perform at least one of the sub-steps of filtering the measurement signals, differentiating the measurement signals to calculate the derivative of the measurement signals, and performing intensity modulation based on the measurement signals. The processing of the measurement signals can vary depending on the type of measurement signal and the determined operating mode. For example, in sub-step S4.2 the first measurement signal 22 can be subjected to different and / or more processing steps than the second measurement signal 26 and vice versa.

[0045] The at least one processed signal is provided to quantify the engine operating parameter. In particular, the processed signal can refer to a value quantifying the average value of the engine operating parameter over the associated time period. Alternatively, the processed signal can refer to a value course over the associated time period.

[0046] Furthermore, in sub-step S4.3 at least one threshold value associated with the at least one processed signal is obtained. In other words, for each processed signal a threshold value is obtained. In this way, the proposed method provides a reference value which allows to qualitatively assess the obtained signal and thus the operation and performance of the engine 16.

[0047] Thus, in sub-step S4.4, each of the processed signals produced in sub-step S4.2 is compared to its associated threshold value obtained in sub-step S4.3. If it is determined in sub-step S4.4 that none of the processed signals reaches its associated threshold value, i.e. exceeds or falls below its associated threshold value, the method returns to step S2. In this case, no unintended performance change of the engine is detected. In other words, if each of the processed signals is within the proper range, i.e. has not reached its associated threshold value, there is no indication of an unintended performance change. This would mean that the engine 16 is working properly, and thus the combustion in the cylinders is working properly.

[0048] Thus, if it is determined that at least one of the processed signals has reached its associated threshold value, i.e. exceeds or falls below its associated threshold value, the method proceeds to sub-step S4.5, in which it is indicated that the engine 16 is subjected to an unintended performance change. In other words, if at least one of the processed signals is outside its proper range, i.e. the range that indicates proper operation of the engine 16, the method makes a decision about the engine 16 being subjected to an unintended performance change. Thereafter, the method proceeds to step S6.

[0049] The configuration and execution of step S4 can depend on the operating mode of the engine 16. Thus, depending on the operating mode determined in step S1, different measurement signals, different processing steps of the respective measurement signals and / or different threshold values can be provided. To illustrate this, embodiments of the method are described in more detail below by reference to the examples of Figure 4 and Figure 5 wherein Figure 4 sub-steps to be executed when the engine is operated in grid parallel operating mode are shown, and Figure 5 sub-steps to be executed when the engine 16 is operated in island operating mode are shown.

[0050] In particular, in a first sub-step S4.0, it is determined whether the engine 16 is operated in grid parallel operating mode. If this is not the case, the method proceeds to sub-step S4.6. However, when it is determined that the engine 16 is operated in island operating mode, the method proceeds to step S4.1a.

[0051] In sub-step S4.1a, only one measurement signal is obtained, i.e. the power measurement signal. In this operating mode, it has been found that it can not be necessary to monitor the engine speed, since the supply frequency is fixed by the grid 12, and thus the engine speed is not expected to change when the engine 16 is subjected to misfires.

[0052] The power measurement signal is then processed to generate a processed signal pS. To this end, the control unit 20 filters the power measurement signal in a step S4.21a in order to eliminate spikes and high frequency noise from the signal. Then, in a step S4.22a, the derivative of the power measurement signal thus filtered is calculated to generate a differential signal. This way, it is possible to monitor sudden changes in the power measurement signal in the time domain.

[0053] In a sub-step S4.3, a threshold value Th associated with the differential signal constituting the processed signal pS is obtained, and in a sub-step S4.4, the threshold value is compared with the processed signal in order to assess whether the measurement signal is within an appropriate range. In case the processed signal pS does not reach the threshold value, i.e. the maximum value of the processed signal pS during the associated time period is lower than the threshold value, the method proceeds to a step S2, thereby indicating that the engine 16 is not subject to an unexpected performance change and thus no misfire condition is detected during the associated time period. However, if the processed signal pS has reached the threshold value, i.e. the maximum value of the processed signal pS during the associated time period is equal to or exceeds the threshold value, the method proceeds to a step S.4.5, indicating that the engine 16 is subject to an unexpected performance change.

[0054] In this configuration, a further step 4.23a (not shown) can be provided, in which an intensity modulation can be performed based on the differential signal in order to determine the amount of change of the power measurement signal and its form. Then, in addition to the comparison performed in step S4.4a above, the amount of change of the power measurement signal is compared with a further threshold value and the form of the power measurement is assessed. Thus, the method can proceed to step S4.5 if the amount of change of the power measurement signal reaches the further threshold value and / or the assessment reveals an inappropriate form of the power measurement signal.

[0055] In the following, the procedure of step S4 is described, in which the engine 16 is operated in an island operation mode. Thus, in a sub-step S4.0 it is determined that the engine is not operated in a grid parallel mode, and the method proceeds to a step S4.6. Then, upon determining in step S4.6 that the engine 16 is operated in an island mode, the method proceeds to a sub-step S4.1, i.e. two sub-steps S4.1a and S4.1b are executed in parallel. Thus, more than one measurement signal is obtained with reference to sub-step S4.1, the more than one measurement signal is processed with reference to sub-step S4.2, and the more than one measurement signal is compared with a threshold value with reference to sub-step S4.4.

[0056] In particular, sub-steps S4.1a to S4.3a are performed in the same way as described above with reference to sub-steps S4.1 to S4.3, respectively. Figure 4The same way is performed to obtain a first processed signal pS_a and a first threshold value Th_a. Sub-steps S4.1 b to S4.3b refer to different types of measurement signals, i.e. the speed measurement signal obtained in sub-step 4.1 b, which is processed in sub-step S4.2b by filtering the speed measurement signal to generate a second processed signal pS_b.

[0057] In sub-step S4.4a, the processed signals are then compared to their associated threshold values. In particular, if the first processed signal pS_a reaches the first threshold value Th_a or the second processed signal pS_b reaches the second threshold value Th_b, the method proceeds to sub-step S4.5.

[0058] In the following, the step S5 of verifying the measurement signals acquired in step S3 is described. As can be gathered from the above, step S5 is performed in parallel to step S4. In step S5, the control unit 20 checks and verifies whether the measurement signals are functional and thus properly represent the operation and functioning of the engine 16. In this way, the condition and functioning of the engine 16 as well as of the sensor units used for the method are assessed to exclude certain fault conditions which can lead to or indicate an unintended change in performance of the engine, but which are not related to misfire conditions. Step S5 can thus also be referred to as a qualification step. Figure 2

[0059] Figure 6 The general procedure carried out during step S5 is schematically shown. In a first sub-step S5.1, the control unit 20 obtains or reads at least one of the measurement signals acquired during step S3. Thereafter, in sub-step S5.2, an appropriate operating range for each of the measurement signals is obtained before the method proceeds to sub-step S5.3. In the shown configuration, the measurement signals are constituted at least by a power measurement signal and a speed measurement signal. Furthermore, further measurement signals are considered and obtained which are indicative of the intake manifold pressure and the differential pressure at the throttle valve.

[0060] In sub-step S5.3, it is determined whether each obtained measurement signal, in particular its value or magnitude, is within the associated appropriate operating range. If this is true, the method proceeds to step S6. If this is not true, the method returns to step S2 and a further analysis or fault detection routine can be initiated.

[0061] ​In step S6, the method detects whether the engine 16 is subjected to a misfire condition, i.e. whether a misfire condition or misfire fault has occurred or is occurring during the associated time period or operating cycle. To this end, the method detects a misfire condition of the engine 16 during operation of the engine 16 by attributing the unexpected change in performance to be caused by a misfire. In other words, in step S6, the unexpected change in performance is causally related to a misfire fault to detect a misfire condition. In particular, to achieve this, the method performs a decision sub-step 6.1 verifying whether an unexpected change in performance was determined in step S5 and whether the measurement signal relied upon is within the proper functional range. If this is not true, the method proceeds to step S2. However, if this is true, i.e. there is an unexpected change in performance and the measurement signal relied upon is within the proper functional range, it is determined or confirmed that the unexpected change in performance is caused by a misfire and the method proceeds to sub-step 6.2 whereby a decision is made and it is indicated that a misfire condition is detected.

[0062] The method then proceeds to step S7 of providing a misfire statistic and thus constitutes a misfire statistic development block. In this step, the occurrence of misfires is monitored during operation of the engine 16 and processed for further use of such information. For example, in this step, the occurrence of misfires can be accumulated over a certain time period, thereby providing a counter function indicating the frequency of occurrence of misfire phenomena over a certain time period during operation of the engine 16. In this way, a misfire statistic can be provided.

[0063] The misfire statistic can be used to determine the proper functioning of the engine 16 and its components, e.g. the ignition system, or to assess whether the engine 16 should be subjected to a maintenance work or further analysis. For example, the control unit 20 can accumulate the occurrence of misfire conditions, e.g. intermittent misfire conditions, occurring during operation of the engine 16 to determine the frequency of occurrence of misfires during operation. Furthermore, the control unit 20 can compare the frequency thus determined to a threshold value and output a signal indicating that the engine is to be subjected to a maintenance work or further analysis when the determined frequency reaches the threshold value.

[0064] All information related to the misfire statistic can be broadcast by the control unit 20 to other components of the engine 16 or systems within or outside the power generating unit 10, e.g. via a CAN bus or Modbus or Ethernet communication link.

[0065] By the proposed method, it is possible to detect misfire conditions occurring during operation of the engine 16 on the basis of measurement values provided by sensor units, which are known to be already equipped with said sensor units. In this way, existing or known hardware configurations can be used to perform the proposed method without the need and use of additional measurement devices, thus providing a cost-effective method. Moreover, the proposed method allows detecting misfire conditions during operation of the engine 16, i.e. while operating the engine 16, thus providing prompt feedback on the operation of the engine 16.

[0066] It will be apparent to those skilled in the art that the described embodiments and implementations are merely examples of a variety of possible implementations. Thus, the embodiments shown herein should not be taken as forming limitations to the features and configurations described. Any possible combination and configuration of the described features can be selected according to the scope of the application.

[0067] The following optional features, among others, can be combined with some or all of the previously mentioned embodiments, implementations and / or features in any technically possible combination.

[0068] The misfire detection method for an internal combustion engine can comprise the step of determining whether the engine is subject to an unexpected performance change, and the step of detecting a misfire condition of the engine by qualifying the unexpected performance change as being caused by a misfire during operation of the engine.

[0069] The proposed method provides a method according to which it is possible to first determine whether an unexpected performance change has occurred during operation of the engine. This step can be performed on the basis of hardware, which is known to be already equipped with, for example, an engine speed sensor or an engine output power sensor. Moreover, this step can be performed during operation of the engine, i.e. in real time or near real time.

[0070] Thereafter, it is possible to determine whether the identified unexpected performance change is caused by a misfire, in order to detect the occurrence of a misfire condition. This step can be performed by monitoring and analyzing engine operating conditions and functions, in particular to verify the measurement signals on which the method is based and / or to exclude malfunction conditions not related or not likely to be related to misfires.

[0071] On the basis of this two-step method, the method allows providing results in real time or near real time, while exploiting hardware, which is known to be already equipped with said hardware and thus does not require adding any measurement devices. As a result, the proposed solution provides a cost-effective method, which allows detecting the occurrence of intermittent misfire conditions, among others, thanks to real-time measurements and misfire detection.

[0072] The proposed method can be used for misfire detection in any suitable internal combustion engine, in particular a reciprocating engine. For example, the method can be used in a stationary gas engine, in particular for power generation. Such a gas engine can be powered with a fuel-air mixture of a gaseous fuel and air, e.g. a mixture of natural gas and air, and can be operated in different operating modes. For example, such a gas engine can be operated in a grid-parallel operating mode and an island operating mode.

[0073] The method can further comprise a step of determining an operating mode of the engine, wherein at least one of the step of determining whether the engine is subject to an unexpected change in performance and the step of detecting a misfire condition is performed in dependence on the determined operating mode. In particular, the step of determining an operating mode of the engine can comprise determining whether the engine is operated in a grid-parallel operating mode or an island operating mode.

[0074] The proposed method can be repeatedly performed during operation of the engine. In other words, the method or some steps or subroutines constituted by at least one step thereof can be initiated or performed at predetermined time periods or events. For example, the method or some steps or subroutines thereof can be performed or associated with at least one operating cycle of the engine or a cylinder thereof. Further, the method or some steps or subroutines thereof can be initiated or performed for each operating cycle of each cylinder. In one configuration, the step of determining whether the engine is subject to an unexpected change in performance is associated with at least one operating cycle of the engine. This means that the method determines whether an unexpected change in performance occurs during the associated at least one operating cycle.

[0075] The step of determining whether the engine is subject to an unexpected change in performance can be performed to determine whether an output torque of the engine is unexpectedly changed, in particular unexpectedly decreased, during operation.

[0076] In particular, the step of determining whether the engine is subject to an unexpected change in performance comprises a sub-step of obtaining at least one measurement signal indicative of at least one engine operating parameter.

[0077] For example, the measurement signal can be indicative of a power output by the engine. To this end, the measurement signal can be determined based on at least one of a current transformer measurement and a voltage transformer measurement performed at a generator driven by the engine.

[0078] Alternatively or in addition, the measurement signal can be indicative of an engine speed. To this end, the measurement signal can be determined based on a pick-up sensor or any other suitable sensor coupled to a crankshaft and / or a camshaft and / or an output shaft of the engine and configured to acquire a rotational speed.

[0079] In a further development, the step of determining whether the engine is subject to an unexpected change in performance comprises a sub-step of generating at least one processed signal by processing the at least one measurement signal. In particular, the at least one measurement signal can be processed by applying at least one of the steps of filtering the measurement signal. Alternatively or in addition, the at least one measurement signal can be processed by applying a step of calculating a derivative based on the measurement signal, i.e. by calculating a derivative of the measurement signal or of a filtered measurement signal. Alternatively or in addition, the at least one measurement signal can be processed by applying a step of performing an intensity modulation based on the measurement signal, i.e. by modulating the measurement signal or a filtered measurement signal or a calculated derivative signal.

[0080] Further, the step of determining an unexpected change in performance can comprise a sub-step of comparing the measurement signal or the processed signal to a threshold value in order to determine whether the engine is subject to an unexpected change in performance or torque.

[0081] In a further development, a step of detecting a misfire condition can be provided such that a measurement signal indicative of at least one engine operating parameter is obtained and compared to an appropriate operating range, wherein a misfire condition is detected when the measurement signal is within the appropriate operating range.

[0082] In addition, the method can comprise a step of providing a misfire statistic, wherein the occurrence of a misfire condition during engine operation is monitored.

[0083] Further, a control unit for a combustion engine, in particular a stationary gas engine, for misfire detection can be provided. The control unit can be configured to determine an unexpected change in performance of the engine and to detect a misfire condition of the engine by attributing the unexpected change in performance to a misfire during engine operation.

[0084] Industrial applicability

[0085] With reference to the accompanying drawings and the description thereof, a method for misfire detection of a combustion engine, in particular of a stationary gas engine for power generation, and a control unit for a combustion engine for performing the method are presented. The method and the control unit as described above are suitable for a combustion engine provided as a stationary gas engine, for example. The proposed method can be performed in or for a conventional combustion engine. Further, the proposed control unit can replace a conventional control unit and can act as a replacement or retrofit part.

Claims

1. A misfire detection method for an internal combustion engine (16), said internal combustion engine (16) being a stationary gas engine for power generation, said method comprising: - Step (S1) to determine the operating mode of the engine (16), wherein the operating mode corresponds to the grid parallel operation mode or the islanded operation mode. - When the operating mode corresponds to the grid parallel operation mode, the power measurement signal of the engine (16) is obtained via the engine output power sensor; When the operating mode corresponds to the islanded operating mode, the power measurement signal and speed measurement signal of the engine (16) are obtained via the engine output power sensor and the engine speed sensor; - Step (S4) to determine whether the engine (16) has experienced an unexpected performance change based on the power measurement signal when the operating mode corresponds to the grid parallel operation mode or based on the power measurement signal and the speed measurement signal when the operating mode corresponds to the island operation mode. as well as - Step (S6) to detect the misfire condition of the engine (16) by identifying the unexpected performance change as caused by a misfire during operation of the engine (16).

2. The method of claim 1, wherein the step (S4) of determining whether the engine (16) has undergone an unexpected performance change is associated with at least one operating cycle of the engine (16).

3. The method according to claim 1, wherein step (S4) of determining whether the engine (16) has undergone an unexpected performance change is performed to determine whether the output torque of the engine (16) has changed unexpectedly.

4. The method according to claim 1, wherein the power measurement signal is determined based on at least one of a current transformer measurement and a voltage transformer measurement performed at the generator driven by the engine (16).

5. The method of claim 1, wherein the step (S4) of determining whether the engine (16) has undergone an unexpected performance change includes a sub-step (S4.2) of generating at least one processed signal by processing at least one of the power measurement signal and the speed measurement signal.

6. The method of claim 5, wherein the power measurement signal is processed by at least one of the following steps: applying a filtering step (S4.21), calculating a derivative step (S4.22), and performing intensity modulation based on the power measurement signal.

7. The method of claim 6, wherein the step (S4) of determining the unexpected performance change includes a sub-step (S4.4) of comparing the power measurement signal or the processed power measurement signal with a threshold to determine whether the engine (16) has experienced an unexpected performance change.

8. The method according to any one of claims 1 to 7, wherein in the step (S6) of detecting the fire condition, at least one of the power measurement signal and the speed measurement signal is compared with an appropriate operating range, wherein a fire condition is detected when at least one of the power measurement signal and the speed measurement signal is within the appropriate operating range.

9. The method according to any one of claims 1 to 7, further comprising the step (S7) of providing misfire statistics, wherein the occurrence of misfire conditions is monitored during operation of the engine (16).

10. A control unit (20) for misfire detection of an internal combustion engine (16), said internal combustion engine (16) being a stationary gas engine for generating electricity, said control unit communicating with an engine output power sensor and an engine speed sensor and configured to: - Determine the operating mode of the engine (16), wherein the operating mode corresponds to the grid parallel operation mode or the islanded operation mode; - When the operating mode corresponds to the grid parallel operation mode, the power measurement signal of the engine (16) is obtained via the engine output power sensor; When the operating mode corresponds to the islanded operating mode, the power measurement signal and speed measurement signal of the engine (16) are obtained via the engine output power sensor and the engine speed sensor; - When the operating mode corresponds to the grid parallel operation mode, the unexpected performance change of the engine (16) is determined based on the power measurement signal or when the operating mode corresponds to the island operation mode, based on the power measurement signal and the speed measurement signal; as well as The misfire condition of the engine (16) is detected by identifying the unexpected performance change as caused by a misfire during engine (16) operation.

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